This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:                3GPP third generation partnership project        CCE control channel element        CQI channel quality indicator        D2D device to device (sometimes termed machine to machine M2M or peer-to-peer P2P)        DL downlink (eNB towards UE)        eNB E-UTRAN Node B (evolved Node B)        E-UTRAN evolved UTRAN        HARQ hybrid automatic repeat request        LTE/LTE-A long term evolution/long term evolution-advanced        MME mobility management entity        NAS non access stratum        PDCCH physical downlink control channel        PDCP packet data convergence protocol        PDU protocol data unit        PUCCH physical uplink control channel        PUSCH physical uplink shared channel        RACH random access channel        RNTI radio network temporary identifier        SR scheduling request        UE user equipment        UL uplink (UE towards eNB)        UTRAN universal terrestrial radio access network        
One example of heterogeneous networks include local D2D communication networks integrated into a cellular network, and there is current research in LTE-A for this to be a deployment of macro, micro, pico and/or femto cells as well as relays in the same spectrum. By example the D2D communications may be among a cluster of devices that are autonomous or semi-autonomous within a cellular network, a grid or group of local machines communicating so as to perform certain tasks in co-operative way, an advanced device acting as a gateway for a number of other low-capability devices or machines to access the network, and co-operative downloading or multicasting within a cluster of devices. A common theme in these examples is that they each utilize a secondary usage of the cellular network for the direct device to device communications.
As with most over the air interfaces, resources are scarce and so control signaling must be done efficiently so that the control signaling overhead is not large in relation to the spectrum available for data transmissions. For a D2D cluster operating under a cellular network, there are instances when the cellular network needs to communicate with the D2D cluster. The network will need to receive control signaling from the individual devices concerning buffer status, CQI reporting, and scheduling requests. Assume for example there is some control information the network sends to the devices on the DL which the network would like to confirm was received by each device in the cluster. There are several approaches to do this.
In one option the network can send control signals to the D2D devices in separate messages, individually to each device in the D2D cluster. In this instance there is no need for the network to specify any identifier for the D2D cluster since the network treats each device as an individual. An advantage is that existing implicit resource mapping can be used for the HARQ ACK/NACK feedback signaling by the devices, in which the ACK/NACK UL resource is mapped from the DL channel on which the message being ACK'd/NACK'd was sent. A disadvantage of this option is that the same information content is transmitted on the DL once for each device in the D2D cluster, which leads to high control signaling overhead.
A second option is for the network to assign some temporary identifier to the D2D cluster and multiplex or concatenate the individual device-specific messages (packet data units PDUs) together and address the combined messages to the cluster. In this option the same control content is still transmitted once over the air interface for each separate device in the D2D cluster, but the advantage is there is no need to generate a common ciphering key to be able to send this common control message. In this option spectrum efficiency is still much less than what experience in signaling for strictly cellular concepts would suggest.
A third option is to transmit the DL control signaling for the D2D cluster in one common control message that is decipherable and decodable by all devices in the cluster. One problem with all these approaches is that the network still needs to know whether both devices received the control message correctly. For the specific implementation in a LTE cellular network, the incorporation of the D2D cluster under the LTE umbrella does not change the normal LTE algorithms, such as how PUCCH resources which are used for sending the UL HARQ ACK/NACK, CQI or SR are implicitly derived from the DL PDCCH CCE index. The existing LTE principles map only one PUCCH resource for an ACK/NACK, but there are multiple devices in the D2D cluster in this example.
Consider conventional control signaling in LTE. A PDSCH transmission from the network implicitly maps related HARQ feedback from a UE onto a specific PUCCH resource. If the UE has PUSCH resources allocated, its HARQ feedback is multiplexed into its PUSCH transmission. 3GPP TS 36.300 v 10.0.0 (2010-June) describes the process as follows. The PUCCH shall be mapped to a control channel resource in the UL. A control channel resource is defined by a code and two resource blocks, consecutive in time, with hopping at the slot boundary. Depending on presence or absence of UL timing synchronization, the UL physical control signaling can differ. In the case of time synchronization being present, the outband control signaling consists of CQI, or ACK/NACK, or a scheduling request (SR). The CQI informs the scheduler about the current channel conditions as seen by the UE. If MIMO transmission is used, the CQI includes necessary MIMO-related feedback. The HARQ feedback in response to DL data transmission consists of a single ACK/NAK bit per HARQ process. PUCCH resources for SR and CQI reporting are assigned and can be revoked through RRC signaling. An SR is not necessarily assigned to UEs acquiring synchronization through the RACH (i.e. synchronized UEs may or may not have a dedicated SR channel). PUCCH resources for SR and CQI are lost when the UE is no longer synchronized.
Clearly the normal LTE HARQ process is not readily adaptable for use with multiple devices operating in a D2D cluster, unless like the first option noted above each device is treated independent of that cluster. The detailed examples below consider how to assign and use UL control resources (e.g., PUCCH) for a group of devices (e.g., a pair or a cluster of more than two devices) involved in D2D communications under control of a cellular network (e.g., an LTE-A network).